In U.S. Pat. No. 5,735,278 (Houllt et al) issued Apr. 7, 1998, is disclosed a medical procedure where a magnet is movable relative to a patient and relative to other components of the system. The moving magnet system allows intra-operative MRI imaging to occur more easily in neurosurgery patients, and has additional applications for liver, breast, spine and cardiac surgery patients.
In U.S. Pat. No. 8,295,905 (Graves et al) issued Oct. 23, 2012 and originally published as 2008/0039712 on Feb. 14, 2008 is disclosed an improvement to the above arrangement where the magnet can rotate about a vertical axis to allow the magnet to be used in adjacent rooms where a diagnostic table associated with the magnet is used in one room and the magnet is used in another room for other intervention where a different table contained within the room is used.
It is well known that the diagnostic table provided for diagnostic MR imaging of patients and typically carried on or with the magnet is unsuitable for other interventions including surgical procedures and radiation treatments.
The arrangement of magnet and diagnostic table manufactured by Siemens under the trade mark Symphony (at a field strength of 1.5 Tesla or 1.5 T) Espree (1.5 T), Verio (3 T) for which the above Hoult and Graves proposal was designed carried a diagnostic table permanently attached to one end. In order to use the same magnet with the diagnostic table at one end it was necessary to rotate the magnet in or for the second room to allow the opposite end of the magnet to be used with the table contained within that room.
In recent years Siemens have introduced a new magnet system under the trade mark Aera (1.5 T) or Skyra (3 T) which is designed to image when the patient is supported by a dockable trolley-like table. The Siemens magnet is arranged to remain at a fixed location for use only with the dockable table and the table can be released from the magnet and moved to a separate location for preparation of the patient for imaging at a location away from the magnet. The trolley-like table is then moved up to the magnet where it docks with a fixed floor mounted docking head for mechanical and electrical connection between the magnet and the table. Once docked, imaging is carried out under control of the imaging computer where signals to and from the table are communicated through the docking head.
When the dockable table is not connected to the system, the scanner will not acquire an MR image (measurement). In this situation, imaging is disabled by design as the clinical workflows considered for scanner use were limited to diagnostic imaging and require a diagnostic-style table connected to the system. The scanner control system detects the absence of a docked table by means of a failure to establish and maintain a defined communications protocol with table components (actuators, sensors, communication buses). When the dockable table is connected, the communication protocol conveys information about different sensor and actuator states. The scanner control system can infer patient position in the scanner bore from these values and system settings such as patient registration (patient age, weight, height, orientation in scanner).
One value that is communicated using the protocol is the position of the patient table within the bore of the MRI scanner. This value, as well as others such as “table in desired position”, is required for safe and effective operation of the scanner. For example, the scanner control system ensures safety of the patient with respect to RF energy absorbed by the patient by calculating and controlling a specific-absorption rate (SAR) setting. The SAR setting is based on many parameters including the patient height, weight, the anatomy to be imaged and the position of the patient table in the bore.
Use of the MRI scanner in a surgical setting, namely an operating room, requires that a surgical table be used to obtain the desired patient positioning for the procedure. The above named dockable tables are not suitable for surgical use due to limited forward/lateral tilt and the lack of mounting points for surgical equipment such as head fixation devices (HFD).
When the above magnet is used in an arrangement of the above Hoult or Graves type installation, the magnet is mounted on ceiling rails and is able to move from one imaging room to an adjacent imaging room. The second table in the second room supports the patient in a combined surgical-imaging position and provides mounting points for surgical equipment.
It is not possible therefore to use the Aera/Skyra (trade mark) magnet of Siemens with the above system of Hoult or Graves since the control system will not allow imaging without the dockable table being properly docked.